Flow ripples or pressure ripples (fluctuations) generated from the hydraulic pump are the source of system vibrations and noises in a hydraulic system. Pressure ripples are also disturbance to motion control that affects the precision and repeatability of the movement.
FIG. 1 illustrates structures and flow ripple patterns of different types of hydraulic pumps. As shown, for the external gear pump, axial piston pump and vane pump, although the required flows are constant, the actual flows fluctuate with rotation of the pumps, which is caused by the mechanical structures of the pumps.
Noises impact human hearing health; vibrations reduce the reliability of the entire system; and the reduced precision directly affects the product quality produced by the hydraulic machine. From every aspect, pressure ripples reduce values delivered to customers. Therefore, pressure ripple reduction has been a core issue that researchers in both academic and industry world have tried to solve.
Most current methods for reduction of flow and pressure ripples are based on novel mechanical designs or additional ripple compensators such as silencers or accumulators. These methods in general suffer from trade-offs among the costs, energy efficiency and system dynamic responses. For example, the method modifying pump shaft design lowers the energy efficiency; adding a pre-compression chamber increases manufacturing and component costs and reduces the efficiency; adding an accumulator or silencer at the pump outlet increases component costs and space, and lowers pump dynamics.
Thus, a solution for reducing noises and vibrations of a pump with higher efficiency and lower costs is needed in the art.